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By Bill Briggs

NFL star Peyton Manning is nearly as famous for his product pitches as his football passes, building an endorsement empire that has included Papa John’s pizza and Oreo cookies. But are your kids grabbing – and consuming – what the quarterback is slinging?

The Denver Broncos signal caller is one of the sports world’s top hawkers of unhealthy foods and drinks, according to a paper published Monday in the journal Pediatrics. The authors are urging famous jocks like Manning to re-think corporate offers to peddle sugar-rich drinks or high-calorie foods.

“Our ultimate hope would be that athletes reject the unhealthy endorsements or, at the very least, promote healthy foods,” said Marie Bragg, lead author of the study and a doctoral student in clinical psychology at Yale University. “These athletes have an opportunity to work with parents. Instead, they’re promoting really unhealthy foods.”

A representative for Manning did not respond to requests for comment. The QB pockets $12 million annually by lending his face, voice and persuasive powers to Buick, Reebok, Gatorade and DirecTV plus Papa John’s – and he owns 21 Papa John’s stores in the Denver area, according to Forbes

On Sept. 29, his pizza-pie profile even ignited some on-field ribbing: During the Broncos’ win over Philadelphia, Eagles defensive players tried to drown out Manning’s play calls by repeatedly screaming the name of the pizza chain. 

But according to the study, one mega-star ranks a notch higher than Manning when it comes to plugging munchies: LeBron James of the NBA champion Miami Heat. He earns $42 million per year by endorsing McDonald’s, Coca-Cola and other products. At No. 3 on the researchers' list of low-nutrient-food boosters is tennis great Serena Williams, who in the past has done ads for McDonald’s and Oreo cookies. Representatives for James and Williams did not respond to interview requests. 

A litany of pro athletes analyzed by the authors put their big names behind 44 different food or beverage brands during 2010, with 79 percent of those food products being “energy-dense and nutrient-poor,” and with 93 percent of the drinks receiving all of their calories from added sugar -- including sports drinks, the paper notes. 

Many of those food-and-beverage sales campaigns are aimed at young consumers. 

“When taking into account the nutrient quality of the products endorsed and the amount of advertising for each product, Peyton Manning, LeBron James, and Serena Williams are the highest contributors to the marketing of unhealthy foods,” the authors wrote.

The promotion of those meals “by some of the world’s most physically fit and well-known athletes is an ironic combination that sends mixed messages about diet and health,” added the authors, who compared the modern players' food peddling to the cigarette ads of bygone sports stars like Babe Ruth and Ted Williams. 

But bashing food endorsements is an unfair swipe, asserts sports-marketing expert John Rowady, because even the opinions among some nutritionists have been known to shift. Consider butter. Diet experts now agree that margarines made of inflammation-promoting, industrial fats are harmful while pastured butter has been shown to slash belly fat and lower heart-attack risk. 

"These athletes become easy picking for advocates pushing different social-change platforms," said Rowaday, president and founder of rEvolution, a sports-marketing and media agency whose clients include Chipotle and Red Bull.

"I guarantee that in a few years (health watchdogs) will say that (smart phones), with all the texting going on, constitutes an unhealthy lifestyle," Rowaday added. "Then you can ask the same question about why LeBron James endorses the Samsung Galaxy?"

One thing is certain: James, Manning, Williams and the like have sparkling selling powers, which is why companies pay them to push their wares. And that's why nutrition advocates like Marie Bragg are concerned about the stars' backing of certain foods and drinks marketed toward kids and teens. 

Two years ago, researchers in Australia found that when sports celebrities endorse energy-dense, nutrient-poor products, some parents begin to perceive that those foods and drinks are actually more nutritious.

"The evidence is that sales go up," said NBC News Health and Diet Editor Madelyn Fernstrom. "So the impact of the athlete endorsements must be working or the companies would not do it."